The phenotypic expression of a transgene in a plant is determined both by the structure of the gene itself and by its location in the plant genome. At the same time the presence of the transgene at different locations in the genome will influence the overall phenotype of the plant. The agronomically or industrially successful introduction of a commercially interesting trait in a plant by genetic manipulation can be a lengthy procedure dependent on different factors. The actual transformation and regeneration of genetically transformed plants are only the first in a series of selection steps which include extensive genetic characterization, breeding, and evaluation in field trials.
Rice production is commonly threatened by various weeds. Some of these can be highly competitive and in cases of severe infestation can result in yield loss of such magnitude that it makes the crop economically unattractive. For direct-seeded, mechanized rice cultivation typical of temperate production, both cultural practices (e.g. crop rotation, irrigation management) and herbicides are necessary to control weeds (Hill et al. 1994, “Aust. J. Exp. Agric. 34:1021-1029”).
The bar gene (Thompson et al, 1987, EMBO J. 6:2519-2523; Deblock et al. 1987, EMBO J. 6:2513-2518) is a gene encoding the enzyme phosphinothricin acetyl transferase (PAT), which, when expresssed in a plant, confers resistance to the herbicidal compounds phosphinothricin (also called glufosinate) or bialaphos (see also for example U.S. Pat. Nos., 5,646,024 and 5,561,236) and salts and optical isomers thereof. Other genes encoding PAT have been described (see for example: Wohlleben et al., 1988, Gene 70:25-37; EP 275,957; U.S. Pat. No. 5,276,268; U.S. Pat. No. 5,637,489; U.S. Pat. No. 5,273,894).
The transformation of monocotyledenous plants by electroporation of intact tissue capable of forming compact embryogenic callus or compact embryogenic callus obtained from such tissue is described in U.S. Pat. No. 5,641,664. Herein, transformation of compact embryogenic callus of rice by electroporation of a bar gene and the regeneration of transgenic rice plants is disclosed.
Transgenic rice plants containing the gus gene with either the bar gene, or the hyg gene conferring resistance to hygromycin, obtained by the transformation of cells of immature rice embryos by bombardment with DNA-coated gold particles have been described (Christou et al. 1991: Biotechnology 9:957).
Transformation of rice with the bar gene by electroporation of aggregated suspension cells is described in U.S. Pat. No. 5,679,558.
However, the foregoing documents fail to teach or suggest the present invention.